In manufacturing semiconductor devices, etching may be performed to form features such as contact holes in a silicon oxide. Further, with miniaturization and high integration of the semiconductor devices, the aspect ratio of such a feature is increasing every year. That is, it is requested that finer and deeper features be formed in the silicon oxide film.
Japanese Patent Laid-Open Publication No. 2007-288119 discloses an example of a method for etching a silicon oxide film. The method for etching a silicon oxide film as described in the Japanese Laid-Open Publication No. 2007-288119 includes exposing a workpiece having a mask on the silicon oxide film to plasma of a processing gas such as, for example, a fluorocarbon gas so as to etch the silicon oxide film. In the method of Japanese Patent Laid-Open Publication No. 2007-288119, an amorphous carbon film is used as the mask.
In such etching of the silicon oxide film, a phenomenon that a side wall defining a hole foil led in the silicon oxide film expands partially transversely, but not vertically may occur. That is, a phenomenon that the width of the hole is increased partially may occur. Such a phenomenon is called “bowing”, and its major factor is that ions or electrons contributing to etching are incident obliquely with respect to holes and collide with the side wall defining the hole. As a method for suppressing the bowing, U.S. Pat. No. 7,977,390 discloses a method for etching a silicon oxide film in which a polysilicon film is used as a mask, and a silicon-containing protective film is formed on a mask surface exposed to plasma, as well as on a side wall of the silicon oxide film which is a hole portion formed on a layer to be etched so as to etch the silicon oxide film while protecting a side wall of a hole from oblique incidence of ions.